February 28, 2009 A variety of solar powered Unmanned Aerial Vehicles (UAV) have been setting world records for flight duration and altitude in recent times, there are even plans for solar powered craft that can remain aloft for years at a time. But it's not just aircraft of the unmanned variety that stand to benefit from solar technology, with planes that carry pilots now starting to take to the skies. Based on glider/sailplane construction methods, the Sunseeker II is the only manned solar airplane flying in the world, and according to SolarFlight, it has logged more time in the air than all other manned solar powered airplanes combined.

Sunseeker II is a hybrid aircraft that uses battery power to take off and increase altitude and can maintain level fight on solar power. The aircraft can also be flown as a glider. As the battery pack is small, the solar cells fully recharge the battery in 90 minutes and with a recharged battery climbing is again possible under power. With its current generation of batteries, solar cells and electronics installed in 2005, the Sunseeker II has never been forced to land before late afternoon.

The team at SolarFlight developed a new technique for integrating the latest generation of solar cells into the actual wing structure rather than bonding them to the surface. The aircraft also features a unique teetering propeller, which drastically reduces vibration and is fitted with four packs of lithium polymer batteries in the wings. The control electronics for the batteries and solar arrays were designed by Alan Cocconi of tzero electric vehicle fame.

Maximum performance is achieved when the aircraft climbs above the clouds and flies on direct solar power in the clear, bright conditions. Under direct solar power, the Sunseeker II is able to fly at 18 m/s (~40 mph) on solar power alone or 36 m/s (~80 mph) when the batteries are also used. It flies slowly enough that it is comfortable to fly with the canopy open. Because of the low speed and the virtual silence of the aircraft birds are not afraid and come very close, matching the plane’s speed, almost landing on the aircraft at times. When the motor is finally shut off, it takes hours to glide down, and the airbrakes are normally needed to get down before dark.

Paul Evans

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